The proposed research involves a study of the enzyme L-aspartase. A range of techniques will be applied in order to gain an understanding of the active site structure, which confers almost total substrate specificity to the enzyme. The catalytic requirements of the enzyme will be examine by determining the features of the substrate molecule that are important for binding and catalysis. The nature of metal ion participation in the mechanism will be examined by binding and kinetics studies. The orientation of substrates and analogs, and the location of metal ion binding sites (monovalent and divalent) will be established by nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) relaxation studies. Knowledge of the active site geometry and reaction mechanism of L-aspartase is important in its own right, and will be helpful in understanding structure-function relationships in enzymes in general. This knowledge may also aid our understanding of the urea cycle enzyme argininosuccinase, which catalyzes a reaction similar to that of L-aspartase, and which has been implicated in an inborn error to metabolism which is associated with mental deficiency.